1. Field of the Invention
The present invention relates to a driving technique of a liquid crystal display for obtaining wide-viewing angle, and more particularly to a liquid crystal display driving apparatus and method capable of improving the viewing angle by converting a gray scale that has poor viewing angle characteristics into a gray scale combination that has good viewing angle characteristics.
2. Description of the Related Art
A liquid crystal display (LCD) controls the light transmittance of a liquid crystal used in the electric field to display a picture. Gate lines and data lines are arranged to intersect in the liquid crystal display, and liquid crystal cells are positioned at the intersection of the gate lines and the data lines. Each of the liquid crystal cells has pixel electrodes and a common electrode for applying an electric field. Each of tile pixel electrodes receives video signals, via a thin film transistor (TFT) that is a switching device.
The liquid crystal alignment state is changed in accordance with the received video signal that controls the light transmittance such that the liquid crystal display displays a picture.
As shown in FIG. 1, an apparatus for driving such a liquid crystal display, includes a gate driver (8) for driving gate lines (G1 to Gn) of the liquid crystal display (10), a data driver (6) for driving data lines (D1 to Dm) of the liquid crystal display (10), a gamma circuit (5) for supplying gamma voltage to the data driver (6), and a timing controller (4) for controlling the gate driver (8) and the data driver (6).
The liquid crystal display (10) includes liquid crystal cells (12) arranged in a matrix shape and thin film transistors (TFT) each formed at the intersection of n pieces of the gate lines (G1 to Gn) and m pieces of the data lines (D1 to Dm). The TFT responds to a gate signal from the gate lines (G1 to Gn) to supply the video signal from the data lines (D1 to Dm) to the liquid crystal cells (12). The liquid crystal cell (12) can equivalently be displayed as a liquid crystal capacity capacitor (Clc) that includes common electrodes facing each other with liquid crystal therebetween and a pixel electrode connected to the TFT.
A storage capacitor (Cst) is formed in the liquid crystal cell (12) and sustains the charged data voltage at the liquid crystal capacity capacitor (Clc) until the next data voltage is charged. The storage capacitor (Cst) is formed between the previotis gate line and the pixel electrode.
The gate driver (8) sequentially supplies gate signals to the gate lines (G1 to Gn) to drive the TFT's connected to the corresponding gate line.
The gamma circuit (5) generates direct current gamma voltage predetermined to have different voltage levels from each other in accordance with a grayscale, that is, the gamma circuit generates the voltage level of the video data signal, and supplies that signal to a data driver (6).
The data driver (6) converts the video data signal to an analogue signal from the gamma circuit (5), and supplies a signal to the data lines (D1 to Dm) by 1 horizontal line per 1 horizontal interval when the gate signal is supplied to the gate line (GL).
The timing controller (4) responds to clock signals, horizontal and vertical synchronous signals, and any other signal from a system driver (not shown) so as to control the driving timing of the gate driver (8) and the data driver (6). In other words, the timing controller (4) responds to the clock signals, the horizontal and vertical synchronous signals, and other signals, and generates gate clock signals, gate control signals. gate start pulses and other signals, and supplies those signals to the gate driver (8). In addition, the timing controller (4) generates data clock signals, polarity reverse signals and supplies those signals to the data driver (6). At the same time, the timing controller (4) synchronizes with the data clock signal and supplies video data of red, green and blue to the data driver (6).
Such a liquid crystal display has the advantages of being small in size, thin and consuming low power. Whereas, its disadvantage is its narrow viewing angle because liquid crystal has an anisotropic property.
There are various proposed methods to form liquid crystal displays having a wide-viewing angle. These proposed methods include the Multi Domain method, Halftone Grayscale method and other methods.
The Multi Domain method divides one pixel area into at least two domains, then sets up the alignment direction of the liquid crystal different from one another in each of the domains to compensate the viewing angle characteristics. However, because the Multi Domain method requires several rubbing processes, its manufacturing process becomes complicated.
The Halftone Grayscale method divides one pixel into at least two areas, and applies different voltages to the areas to obtain grayscale, thereby improving the viewing angle characteristics. Generally, the liquid crystal in Twisted Nematic mode (hearafter TN mode) shows worse viewing angle characteristics at the middle grayscale than at black or white grayscale.
To solve this problem, the Halftone Grayscale method divides the middle greyscale (i) having a poor viewing angle characteristic into two sub-areas (12A, 13B), as shown in FIG. 2B. FIG. 2A shows a pixel (12) of a general grayscale method. More particularly, the Halftone Grayscale method applies different voltages to each of the sub-areas (12A, 12B) of the grayscale (A, B). And the middle grayscale is formed from the sum of the grayscales (A+B) improving the viewing angle.
Although the Halftone grayscale has the advantage of improving the viewing angle characteristic due to the larger number of sub areas in one pixel, resolution deteriorates according to the number of space divisions of the pixel area. Also, because the Halftone grayscale method mostly uses a floating pixel electrode and an insulating layer for applying the different voltages from one sub-area to another, the Halftone grayscale method requires additional manufacturing processes for forming the pixel electrode. Also, voltage-light characteristics differ from each sub-area where the floating electrode is located resulting in a brightness difference between the sub-areas where the same voltage is applied, resulting in deteriorated picture quality.